The vast majority of voltage regulators (converters) used in high performance electronics may be classified into two basic types: linear and switched regulators. Switched regulators are much more efficient than linear regulators because the pass transistors used in switched regulators do not continuously draw current. The best efficiency achievable with a linear regulator, even assuming ideal (lossless) components, is Vout/Vin, where Vout is the regulated output voltage and Vin is the input voltage to the voltage regulator. Linear regulators may be a good choice for applications in which the difference between the output voltage Vout and the original supply input voltage Vin is not too large. But when the regulated voltage is sufficiently less than the input voltage, switched regulators are usually the preferred option, particular where power savings is important.
Switched regulators making use of inductors, such as a Buck switching regulator, can offer an operating efficiency greater than 90%. Presently, such voltage regulators are not fully integrated on the processor die for several reasons. Voltage regulators are usually designed with operating frequencies in a range of 0.1 to 10 MHz. But the inductance needed for switched voltage regulators using inductors operating in this frequency range is too large for an on-chip inductor. Increasing the operating frequency still leads to inductors that are too large for on-chip placement without the use of magnetic material in the inductor. However, magnetic materials are typically not used in high-frequency inductors because their frequency range has to date been limited to much less than 100 MHz.
As processor technology scales to smaller dimensions, supply voltages to circuits within a processor will also scale to smaller values. The power consumption of processors has also been increasing. Using an external power supply or an off-chip voltage regulator to provide a small supply voltage to a processor with a large power consumption will lead to a larger total electrical current being supplied to the processor. This will increase the electrical current per pin, or the total number of pins needed. Currently, the number of pins limits the scaling of ULSI circuits. An increase in supply current can also lead to an increase in resistive voltage drops across various off-chip and on-chip interconnects.
Furthermore, there has been interest in using two different supply voltages in a processor to reduce power consumption and pin count. As an example, a processor may be designed so that high performance circuits within the processor use a higher supply voltage than that used for low performance circuits within the processor. Modeling has shown that at least a 30% savings in power can be achieved by using a dual power supply in a microprocessor. Using one or more off-chip voltage regulators to provide two circuit supply voltages to a processor die can lead to an increase in complexity, pin count, and cost.
Consequently, as technology scales to smaller voltages, and for dual voltage processors, there would be advantages to integrating switched voltage regulators on the die.